The present invention relates to circuit breakers and more specifically to gas insulated circuit breakers utilizing pull rod arrangements for effecting the operation of the circuit breaker contacts of each of the phases. It has been the practice of providing accelerating openings for each pull rod of each phase with the accelerating springs extending externally of the external pull rod box. This arrangement is both unsightly and is subject to damage. For providing a check on the operating characteristics of the breakers, such as the opening velocity of the circuit breaker contacts, it has been necessary to breach the integrity of the gas sealed enclosures to connect necessary apparatus to the contacts of each of the phases. This, of course, requires a relatively long outage of the breaker for accomplishing the required testing. It has also been the practice of providing a gas system for the gas insulated circuit breakers which required a maze of piping that, of course, required a multitude of joints which are highly subject to leakage. Since the gaseous dielectric medium utilized in these types of circuit breakers, such as sulfur hexafluoride, is relatively expensive, loss due to leakage must be avoided both to reduce the cost factor and maintain the integrity of the system.